A thermal anemometer is a wind measuring instrument based on a heated element, such as a heated wire. The underlying principle of operation of a heated wire thermal anemometer is that the resistance of the wire changes as heat is removed by the air flowing over the wire. Thermal anemometers generally require complex circuits such as a Wheatstone bridge inside of a closed loop analog servo that controls the voltage applied to the bridge circuit. A variable voltage powers the top of the bridge and a control loop adjusts the voltage to keep the bridge in balance. A variable voltage measured across the bridge can then be converted into a wind speed.
What is needed is an inexpensive circuit topology that can measure small wind speeds.